In the past, various measures have been taken in order to increase a transmission capacity (hereinafter, also referred to as “system capacity”) in a communication system. For example, in a third generation partnership project long term evolution (3GPP LTE), a technique for increasing the system capacity using a “small cell” in addition to a “macro cell” has been discussed. Here, a “cell” is defined based on a “communication area” and a “channel frequency” of one base station. The “communication area” may be an entire area that a radio wave transmitted from a base station can reach with a predetermined power value or higher (hereinafter, also referred to as “range area”), or alternatively, may be a divided area obtained by dividing the range area (so-called sector). On the other hand, the “channel frequency” is one unit of frequency used by a base station for communication and defined based on a center frequency and a bandwidth. In addition, the channel frequency is part of an “operating band” assigned to an entire system. Meanwhile, the “macro cell” is a cell of a base station capable of transmitting with a higher transmission power (macro base station), that is, a base station having a larger range area. Compared to this, the “small cell” is a cell of a base station that transmits with a lower transmission power (i.e., a small-cell base station), that is, a base station having a smaller range area. Furthermore, a network in which a plurality of base stations with different transmission power or of different types coexists, as described above, is sometimes called “heterogeneous network”. Examples of the small cell include a pico cell.
Here, in the heterogeneous network, there is a case where a problem is caused by, for example, a terminal in the macro cell interfering with a terminal or a base station in the small cell. As a technique for suppressing such interference, for example, a technique called inter-cell interference coordination (ICIC) has been proposed. In the ICIC, the macro base station prepares a resource whose assignment to a terminal being connected to that macro base station is limited (that is, a “resource not to be assigned”) to reduce the interference in that resource with the small-cell base station or a terminal being connected to the small-cell base station. In a 3GPP Release 8, for example, a high interference indicator (HII) serving as an X2 interface is defined. By using the HII, a resource of a terminal significantly interfering with an adjacent cell can be notified to the adjacent cell.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2011-091783    [Patent Document 2] Japanese National Publication of International Patent Application No. 2012-511295    [Patent Document 3] Japanese Laid-open Patent Publication No. 2012-231217    [Patent Document 4] Japanese National Publication of International Patent Application No. 2011-515916
Incidentally, in the small cell, a resource corresponding to a resource not to be assigned in the macro cell functions as a resource to be assigned in the small cell, whereas a resource corresponding to a resource to be assigned in the macro cell functions as a resource not to be assigned in the small cell.
In other words, according to the related ICIC, part of resources in the small cell is not usable and thus the available resources in the small cell are decreased. As a result, throughput is reduced.